1. Field of the Invention
This invention relates to a process for producing hydrogen by reacting carbon monoxide with steam at elevated temperatures in the presence of a catalyst containing at least one alkali metal compound, at least one metal hydrogenation-dehydrogenation component and a halogen moiety. More particularly, the invention relates to an improved water gas shift catalyst that contains a halogen constituent, preferably chemically combined chlorine, in combination with an alkali metal salt derived from a weak acid and at least one metal hydrogenation-dehydrogenation component and processes utilizing the chlorine-containing catalyst for the production of hydrogen.
2. Description of the Prior Art
It is well known in the prior art that hydrogen can be made commercially by either of the following catalytic reactions: EQU CH.sub.4 + H.sub.2 O .revreaction. CO + 3H.sub.2 ( 1) EQU co + h.sub.2 o .revreaction. co.sub.2 + h.sub.2 ( 2)
reaction (1), often called the steam reforming reaction, relates to converting a hydrocarbon to hydrogen and carbon dioxide in the presence of steam. Reaction (2), often referred to as the water gas shift reaction, relates to a process for converting carbon monoxide to hydrogen and carbon dioxide in the presence of steam. It is also known that reactions (1) and (2) are entirely different from one another, each having their own developed body of art. For example, reaction (1) is endothermic while reaction (2) is exothermic. In addition, reaction (1) is favored by higher temperatures than reaction (2). (See Kirk-Othmer Encyclopedia of Chemical Technology, 2nd edition, H. F. Mark, J. J. McKetta, and O. F. Othmer, eds., Vol. 2, Interscience Publishers, New York, 1963, pp, 275-277.)
The water gas shift reaction, the predominant reaction occuring in the present invention, is typically promoted with catalysts based on combinations of iron oxide with chromia or mixtures of copper and zinc materials. The currently used commercial shift catalysts suffer from a number of deficiencies, the principal deficiency being the inability of the available catalysts to promote the shift reaction to high conversion levels when the process is conducted at low temperatures in the presence of sulfur and/or halogen impurities.
One of the inventors named herein has discovered that the problems encountered with the use of prior art water gas shift catalysts could be overcome by utilizing a shift catalyst based on a combination of an alkali metal compound derived from an acid having an ionization constant less than about 1 .times. 10.sup.-3 with at least one metal hydrogenation-dehydrogenation component. It was found that unusually effective results could be secured with this catalyst when the weight ratio of the hydrogenation-dehydrogenation component to the alkali metal compound, each measured on the basis of the oxide thereof, present in the catalyst is maintained at levels of less than about 10:1, preferably less than about 5:1, and most preferably less than 3:1. The activity of this type of catalyst was found to be further enchanced when at least a portion of metal hydrogenation-dehydrogenation component and/or alkali metal compound are present in the catalyst in a sulfide form. However, the very high activity level secured with the sulfided catalyst slowly degrades with use unless the feedstock being processed contains at least minor amounts of sulfur constituents.
Shift catalysts containing metallic hydrogenation-dehydrogenation components in combination with minor amounts of alkali metal materials have been described in British Patent No. 961,860 and U.S. Pat. No. 3,529,935. Numerous other references exist that disclose catalyst combinations made up of heavy metal compositions in conjunction with an alkali material. Exemplary of such teachings are the disclosures of Switzerland Patent 69,336; U.S. Pat. Nos. 1,330,772; 3,518,208; 3,490,872; 1,896,840; 2,147,780; 2,364,562; Ztschr. Elektrochem 44 (1938), pp. 577-578; Netherlands application 66,01536; Japanese Pat. No. 129,729; Russian Pat. No. 67,942; French Pat. Nos. 777,546 and 815,351; Austrian Pat. Nos. 149,657 and 153,165; German Pat. No. 706,868; Belgian Pat. No. 659,421 and Simck et al., Zprary Ustava Ved. Vyk, Uhli Praze, 2 (1935) pp. 113-128 (see also Chem. Abs., 30 (1936)).
Another reference, U.S. Pat. No. 2,013,066 relates to the production of hydrogen by reacting a hydrocarbon with steam. The patentee also discloses a process for the simultaneous reaction of reactions (1) and (2), that is the simultaneous catalysis of the reaction of steam with a hydrocarbon and carbon monoxide to produce hydrogen and carbon dioxide, at a reaction temperature that varies from about 500.degree. to about 750.degree. C. This temperature range, which is indicative of the higher temperatures employed in the stream reforming reaction, is outside the range of the temperatures used in the water gas shift reaction, the predominant reaction of the present invention.